Ion-based smoke detectors include an ionization or ion chamber. The ionization chamber may be located on, or have solder connections to, a printed circuit board (PCB). The ionization chamber (e.g., a collector plate within the ionization chamber) may be coupled to an integrated circuit (IC). The IC may condition and/or process the output of the ionization chamber to determine whether a detected condition (e.g., presence of smoke) should be indicated. For example, the IC may include a comparator that compares the output of the ionization chamber to a reference threshold for purposes of indicating whether excess smoke is present. In some instances, a microcontroller and analog-to-digital converter (ADC) may be used to process the output of the ionization chamber.
Given the low level signaling (e.g., nanoamps, picoamps, etc.) that is used in smoke detector applications, leakage currents pose significant challenges. For example, leakage currents may contaminate the signal output of the ionization chamber if not minimized or controlled. Conventionally, the IC has been fabricated using a dual inline package (DIP). One pin of the DIP is bent up, and a flying lead is soldered between the pin and the ionization chamber. The use of the flying lead helps to avoid leakage that would otherwise result from, e.g., processing/contaminant in connection with the PCB. The bent pin/flying lead configuration effectively serves as an electric fence and guards against leakage, such that the only measurable leakage would be present on the DIP itself.
While the use of the bent pin/flying lead configuration may be effective in reducing leakage, its use imposes additional manufacturing costs and requirements. Moreover, the bending of the pin exposes the IC to a degraded mechanical integrity. Furthermore, technology is generally tending to shift away from DIP and towards surface mount packaging. Continuing to use the bent pin/flying lead configuration associated with DIP will become prohibitively more expensive as fewer DIP ICs are available. Surface mount packages also tend to be smaller or denser than DIP, leading to an increase in leakage current.